The present invention relates to an electronic system and a method for reducing power supply voltage which is supplied by a voltage regulator to an electronic device, in order to protect the electronic device when a certain failure occurs to the electronic device.
Electronic devices such as electronic endoscopes are desired to be equipped with a power supply interruption system for interrupting power supply voltage which is supplied to a particular circuit of the electronic device (e.g., a CCD and a CCD driving circuit of the electronic endoscope) in order to protect the circuit when the certain failure occurred to the electronic device.
FIG. 3 is a circuit diagram showing an example of a conventional power supply interruption system. The power supply interruption system of FIG. 3 controls power supply voltage which is supplied to a CCD circuit, including a timing generator 140, an inverter 150, a CCD driving circuit 160 and a CCD 110, provided in an electronic endoscope (i.e., an electronic device). A preset DC voltage generated by a power supply 103 is converted by a regulator unit 120 into a proper DC power supply voltage. The DC power supply voltage converted by the regulator unit 120 is supplied to the CCD circuit.
The switching element 130, being operated by a control signal S1 supplied from a CPU (Central Processing Unit) 170, controls the conduction/interruption of electric power supplied from the regulator unit 120 to the timing generating circuit 140, the inverter 150, the CCD driving circuit 160 and the CCD 110. A pulse signal generated by the timing generating circuit 140 is inputted to the CCD driving circuit 160 via the inverter 150. The CPU 170 has a function for determining whether or not failure has occurred to the electronic device of the electronic endoscope.
When a certain electronic failure occurs in the electronic endoscope, the CPU 170 operates the switching element 130 and thereby interrupts the power supply voltage supplied from the regulator unit 120 to the timing generating circuit 140, the inverter 150, the CCD driving circuit 160 and the CCD 110. By the mechanism, the power supply voltage and the pulse signal which are inputted to the CCD driving circuit 160 are interrupted in case of the certain failure of the electronic endoscope, by which a particular circuit (CCD driving circuit 160 and CCD 110) is protected.
As described above, the conventional power supply interruption device protects the particular circuit of the electronic device by turning the switching element off when the certain failure is found. However, due to the switching element connected in series with the power supply line supplying electric power to the particular circuit to be protected in case of failure, constant voltage drop is caused by the resistance of the switching element in the normal state (normal operation) of the electronic device.
Further, individual difference of the switching element makes the setting of power supply voltage complicated and troublesome. In addition, since the switching element is connected in series with the line supplying electric power to the parts, an expensive power device has to be used as the switching element, by which manufacturing cost of the electronic device increases.